Copper-based bearing material and sliding bearing for internal combustion engines

ABSTRACT

The copper-based sliding material has improved seizure resistance, even if it is free of Pb, and enables thinning of the overlay. The copper alloy provided consists of from 0.1 to 2% of Ag, from 1 to 10% of Sn, and the balance consisting of Cu and unavoidable impurities and, further said Ag and Sn do not essentially form the secondary phases but are in complete or essentially solid-solution state in the Cu matrix.

This is the national stage of PCT/JP96/03118 filed on Oct. 25, 1996.

TECHNICAL FIELD

The present invention relates to copper-based sliding bearing materialand sliding-bearing material for internal combustion engine. Moreparticularly, the present invention relates to a copper-basedsliding-bearing material having novel composition and structure, andused for the bearings of internal combustion engines, such as the mainbearings of the engine and connecting-rod bearings, as well as thesliding bearings, such as the main bearings of an engine andconnecting-rod bearings, for which the above material is used.

BACKGROUND TECHNIQUE

Heretofore, the general sliding bearings of an internal combustionengine are, as is described in Japanese Unexamined Patent Publication(Kolai) No. Sho 60-145,345, provided by sintering a copper-alloy, i.e.,the so-called lining, which consists of from approximately 8 to 35% ofPb, not more than approximately 10% of Sn, and the balance consisting ofCu, on a strip consisting of low-carbon steel, such as SAE 1010 and1020.

Furthermore, as is described in detail in Japanese Patent Divulgation(Kohyo) No. Hei 1-503,150, Sn diffuses into the lining of a bearingstructure with a Pb--Sn based or Pb--Sn--Cu based overlay on the lining,with the result that Sn is so depleted in the overlay as to drasticallydeteriorate the corrosion resistance against the lubricating oil. An Nibarrier has, therefore, been sandwiched by plating between the liningand the overlay. The proposal in the publication mentioned above as acountermeasure against the corrosion attributable to lead resides in therefinement of the lead phases.

The lead, which is contained in the conventional overlay-fitted kelmetbearing, is a soft metal and has an excellent sliding property andconformability. Therefore, lead, which realises the conformability, hasbeen used for the purpose of preventing the seizure due to adhesion ofCu.

When the conventional sliding bearing is used in degraded lubricatingoil for extended periods of time, and the lining is then exposed, thelead phases of the lining are corroded and dissolved, thereby rougheningthe lining surface and hence leading to seizure. Alternatively, sincethe lead phases are dissolved out, thus forming pores, the strength ofthe lining is lowered, leading to collapses of the lining, therebyincurring seizure. A measure to refine the lead phases has beenundertaken to mitigate the corrosion of lead phases. However, thismeasure involves limitations arising from the use of lead insofar as thesliding bearing materials contain lead.

In addition, when the conventional sliding bearing is used in degradedlubricating oil for extended periods of time, copper reacts with thesulfur (S) in the lubricating oil and is sulfurized to form coppersulfide on the lining surface. As a result, the corrosion resistance andwear resistance detrimentally deteriorate. As a measure against thisdeterioration, Zn addition is implemented. However, the addition of Znvirtually has no effect on enhancement of the seizure resistance.

Furthermore, the conventional overlay is 20 μm or more thick so as tonot only provide conformability with the shaft but also to exhibit thesliding-bearing performances, such as seizure resistance, due to theoverlay itself. It is, however, needless to say that thick platingshould be avoided from the point of view of the cost of sliding-bearingmaterials.

There is a problem from another point of view. That is, although theconventional nickel barrier must be used for preventing the Sndiffusion, when the nickel barrier is exposed due to the wear ofoverlay, seizure becomes extremely liable to occur on the exposed hardNi portions. This result has been occasionally judged to be the life ofa bearing. Although such problems of the Ni barrier have been pointedout heretofore, it can be said that the use an Ni barrier is inevitablefor preventing the tin diffusion.

DISCLOSURE OF INVENTION

The present invention provides a copper-based sliding bearing materialand sliding bearing for internal combustion engine which can solve theabove-described various problems.

The present first invention is a copper-based sliding bearing materialhaving improved seizure resistance, characterized in that it consists,by weight percentage, of from 0.1 to 2% of Ag, from 1 to 10% of Sn, andthe balance consisting of Cu and unavoidable impurities and, further,said Ag and Sn do not essentially form the secondary phases but are in acomplete or essentially solid-solution state in the Cu matrix.

The present second invention is a sliding bearing for the internalcombustion engine which comprises the above-mentioned copper-basedsliding material and an overlay of from 1 to 25 μm thickness whichconsists of soft metal or solid lubricant and resin.

The present third invention is a sliding bearing for the internalcombustion engine, in which the above-mentioned overlay is directlybonded on the above mentioned sliding-bearing material withoutintermediary of an intermediate layer.

The constitution of the present invention is described hereinafter.First, the alloy composition of the sliding bearing material accordingto the present invention is described.

Ag, which is contained in the copper-based alloy, is dispersed uniformlyand finely in the Cu matrix, thereby enhancing the seizure resistance.In any case that the Ag content is less than 0.1% or exceeds 2%, noeffect of enhancing the seizure resistance is attained. The preferableAg content is from 0.4 to 1%.

Next, the solute Sn enhances the hardness and strength of the Cu matrixand also improves the corrosion resistance and adhesion resistance. Whenthe Sn content is less than 1%, no improving effect of adhesionresistance is attained. On the other hand, when the Sn content exceeds10%, the copper-based alloy becomes too hardened and its conformabilityas a bearing becomes poor. In addition, precipitation of Cu₃ Sn compound(ε phase) starts to impair the seizure resistance. Preferable Sn contentis from 2 to 7%.

Not more than 0.5% of P may be further added to the above mentionedcomposition. Although P in itself does not particularly contribute tothe sliding properties, it acts as a deoxidizing agent and improves themelt flowability at the powder atomizing. The properties of the powderare, therefore, improved. P enables sintering at a relatively lowtemperature as well. In addition, P exerts an effect as the deoxidizingagent in the production of cast material and improves the meltflowability, thereby lessening casting defects. The amount of soluteoxygen, which may impede the precipitation of Ag and Sn during use of abearing, is decreased by the P addition. The amount of Sn and Agmaintained at the solute state is so increased by the P addition as toimprove the seizure resistance. The P addition is, therefore, preferablein a case where the oxygen amount in the copper alloy is large. However,when the P content exceeds 0.5%, the copper alloy becomes hard andembrittled. The preferable P content is from 0.05 to 0.15%.

The particularly preferable composition is Cu-1% Ag-5% Sn, the Ag and Sncontents of which exceed the solid-solubility limits under theequilibrium state. The alloy, in which these elements are forcedlysolid-dissolved, exhibits markedly improved sliding properties.

The elements other than the above-mentioned ones are such impurities asO, Fe, As and Ni ordinarily contained in the copper. The lower thecontents of these elements, the better. Particularly, the oxygeninvolves a danger of impeding the precipitation of the forcedlysolid-dissolved Ag (c.f. FIG. 3 described later). Pb brings about thecorrosion by the S component in the lubricating oil. Therefore, the lessO and Pb, the better. Since the other elements bring about noadvantageous effects, it is preferable to control to approximately 1% orless in total. It is to be particularly noted that, although Pb, whichis soft metal, is not contained as an essential element, in thecopper-based alloy according to the present invention, Cu does notadhere on the opposite material and has markedly improved slidingproperties. However, not more than 4% of Pb and Bi may be added to thecopper-based alloy in order to impart free cutting property.

Subsequently, the structure of the copper alloy according to the presentinvention is described.

In the present Cu--Sn--Ag based alloy, the solid-solubility limits underthe equilibrium state is approximately 2% for Sn and approximately 0.2%for Ag. The alloy composition of the present invention extends,therefore, over a range less and more than the solid-solubility limitsof these elements.

It is important for improving the sliding properties that these elementsare solid-dissolved in the Cu matrix and are finely dispersed within thedetection level of an electron microscope. The complete solid-solutionstructure in the present invention means that an electron microscopedoes not detect any presence of the secondary phases and, further, EPMAdoes not detect any concentration of Cu, Sn, Ag and P resulting in theformation of the secondary phases such as Ag, ε-CuSn_(x) (Cu₃ Sn), and5-CuSn (Cu₆ Sn₅). It is required in the present invention that suchprincipal components as Cu, Sn and Ag do not form the secondary phases,while the impurities may form inclusions or secondary phases in a traceamount without causing any in convenience.

In the present invention, the solid-solution state is desirably acomplete one but may be an essential one, in which the secondary phasesare virtually not detected. Specifically, the essential solid solutionstate herein indicates that, when an X-ray image photograph of therespective elements such as Ag are observed by an image analyzingdevice, the secondary phase is 5 area % or less at an optionalobservation field (magnification of 1000 times).

As is described in detail hereinbelow, Ag is concentrated on the bearingsurface during the use of a bearing and forms an Ag--S compound. Thisphenomenon seems to be a reason why the sliding properties of thesliding-bearing material according to the present invention areoutstandingly improved. Since it is the above mentioned solid solutionstate of the Cu matrix that enables the formation of an Ag--S compound,the solid solution state should be detected in the lining except for theuppermost surface. In addition, since the solid-solution state is anecessary condition for improving the sliding properties during use of abearing, the solid solution state should be realized in a shallow regionof a bearing, where the wear of a bearing is likely to occur, that is,approximately 1 μm deep from the surface. Ag and the like may beprecipitated in the material interior, where the cooling rate becomesslow due to the mass effect when the material is rapidly cooled. This isto be made clear in the description hereinafter.

It is necessary for solid-dissolving the Ag and Sn into the Cu matrixthat the sintering is carried out at preferably from 800 to 900° C.,followed by rapid cooling at a cooling rate of 50° C./minute or higher,or the solution heat-treatment is carried out under the same conditions.These elements should, thus, be forcedly dissolved in the Cu matrix.

In the case of cast materials, the melt is blown, within N₂ atmosphere,onto an approximately 1.5 mm thick steel sheet (SPCC) which has beenpreliminarily heated to approximately 500 to 600° C. Subsequently, thesteel sheet is preferably water-cooled from the back side at a coolingrate of 100° C./second or more.

As is described hereinabove, the Ag and Sn contents are occasionallyless than the solid-solubility limits under the equilibrium state. Rapidcooling is desirable as well so as to prevent segregation of theelements.

Subsequently, the sliding bearing, in which the sliding-bearing materialaccording to the present invention is used, is described. Thissliding-bearing material can be used in every known form, such as anoverlay-utilizing form, as conventionally. Particularly useful methodsfor using the sliding-bearing material having very excellent slidingproperties according to the present invention are as follows.

Since the sliding-bearing material according to the present inventionneed not be supplementarily reinforced by a thick overlay, as in thecase of conventional material, the thickness of the overlay may be ofsuch a level as required for providing conformability with a shaft, thatis, from 1 to 25 μm, preferably from 2 to 8 μm.

Various metallic overlays, such as Pb--In, Pb--Sn--Cu, Pb--Sn--In,Pb--Sn--In--Cu based alloy plating, Sn-based plating, and In-basedplating can be used. In addition, an overlay, in which the solidlubricant such as MoS₂ is bonded with resin binder such as polyimide(PI), polyamide imide (PAI), epoxy resin and the like, can be used.

As is described hereinabove, there occurs during use of a bearing aphenomenon such that the Sn contained in the overlay diffuses into thelining. Since the overlay may merely have the function to provideconformability in the present invention, the performance of the overlayneed not be maintained for such a long period of time that the Sn isdepleted. From this point of view, the nickel barrier becomesunnecessary. Furthermore, by means of positively omitting the nickelbarrier, the seizure due to the exposed nickel barrier can be prevented,and excellent seizure resistance of the exposed lining can even beutilized. In such sliding bearing, the surface of the copper-basedsliding-bearing material may be treated by etching, shot blasting,plating and the like for enhancing adhesion of the overlay.

Phenomena, which are recognized when the copper-based material accordingto the present invention (1) and the comparative copper-based material(2) are used as a bearing, include the following. (a) The solute Ag inthe matrix precipitates on the sliding surface during use of a bearing(temperature: 120-180° C.) and are reacted with the S component in thelubricating oil to form an extremely thin film of Ag₂ S which is anAg--S compound (1). (b) Precipitation of Ag is not detected in thelining interior 1 μm or more under the sliding surface (1). (c) The Agprecipitated from the initial period of use of a bearing is too hard andhas poor sliding properties. The above mentioned Ag₂ S film is notformed widely and uniformly and the sliding properties are, therefore,not improved (2). (d) Even when the Ag content is less than thesolid-solubility limit, the phenomenon (a) occurs (1).

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing the relationship between the Ag content andthe area ratio of the Ag-precipitating portions.

FIG. 2 is a graph indicating the relationship between the Ag content andthe seizure load.

FIG. 3 is an SEM image of Ag of the copper-based material containing 4%of Ag.

FIG. 4 shows a stick-slip tester.

FIG. 5 shows a seizure tester.

BEST MODE FOR CARRYING OUT THE INVENTION

Sintered materials, with a composition of Sn=5%, P=0.05%, Ag≦5%, thebalance of Cu, was produced by the same method as in Example 1 describedhereinbelow. The Ag precipitating area ratio was measured in five fieldsbefore using as a bearing. The result is shown in FIG. 1. The seizureload of these materials are shown in FIG. 2. In FIG. 3 is shown an SEMimage of Ag (magnification of 1000 times) for a composition of Ag=4% andAg-precipitating are a ratio=4%. The following facts are revealed fromFIGS. 1 and 2. (a) Ag is in completely solid-solution at 1% or less. Theseizure load outstandingly increases with the increase in the Ag contentin a completely solid-solution state of Ag. (b) When the Ag contentexceeds 1.0%, the forced solid-solution becomes impossible, and the Agprecipitation starts. Along with this, the seizure load graduallydecreases. (c) At the upper limit of Ag, i.e., 2%, 1% of Ag is presentas a solute, while the residual 1% of Ag is present as the secondaryphase. Even if the structure is under such a state, the seizure load ismaintained at a very high level due to the effect of solute Ag.

FIG. 3 shows one example of precipitation morphology of the Ag secondaryphase.

Meanwhile, Sn also improves the seizure resistance, provided that it isa solute element of the Cu matrix. When Sn precipitates as the secondaryphase before the use of a bearing, hardening and embrittlement occurs sothat the sliding properties are impaired. The copper-based alloy havingthe inventive characterizing structure contains a solute Sn, which thenprecipitates on the sliding surface during use of a bearing.Furthermore, Ag is also together precipitated in a precipitation site ofSn. Such compounds as Ag₂ S, Ag₃ Sn, SnS and the like are, therefore,formed as the secondary phases on the sliding surface. Presumably, thesecompounds improve the sliding properties.

The present invention is described more in detail by way of examples.

EXAMPLE 1

The alloy melt having the composition shown in Table 1 was pulverized byatomizing. The powder, particle size of which is 150 μm, was dispersedon a backing steel sheet (SPCC, thickness=1.4 mm) to a thickness ofapproximately 0.6 mm. The powder was sintered at 850° C. in a hydrogengas atmosphere, without compression. Rapid cooling was subsequentlycarried out at a cooling rate of 50° C./minute. Subsequently, thesintered layer was compressed to reduce the entire thickness to 1.5 mm.The surface of the sintered material was polished to obtain roughness of0.5 μm. The so-prepared specimens (thickness of 1.5 mm) were subjectedto the stick-slip test. The testing method is illustrated in FIG. 4 andis pertinent for examination of the tendency of seizure occurrence dueto adhesion. In FIG. 4, 1 is a testing specimen, 2 is a heater, and 3 isa steel ball being displaced on the specimen surface while imparting theload. The testing conditions were as follows.

(a) Load (W): 500 g

(b) Radius of steel ball at its tip end: 4 mm

(c) Displacing speed of steel ball: 3.6 mm/min

(d) Displacing distance of steel ball: 20 mm

(e) Highest heating temperature by heater: 200° C.

(f) Measurement of adhered area of copper: by the surface photograph ofsteel-ball surface

The results of the stick-slip test are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                                             Occurring                                                                     Time of                                                                       Stick Slip                                                                      Occ-                                                                          uring          Cu                                                             Tem-   Coef-   Ad-                                     Composition            pera-  ficient hered                                   (wt/%)                 ture   of      Area                                    No.       Cu    Ag     Sn   Pb  P    (° C.)                                                                      Friction                                                                            (μm.sup.2)                 ______________________________________                                        Examples                                                                             1      Bal   0.5  5    --  0.03 None --      0                                2      Bal   1.0  3    --  --   None --      0                                3      Bal   1.5  7    --  0.05 None --      0                                4      Bal   2.0  10   --  0.08 None --      0                                5      Bal   0.1  1    --  --   None --      0                         Comp-  6      Bal   --   --   --  --   100  0.40  2000                        arative                                                                              7      Bal   0.05 --   --  0.1  120  0.42  1700                        Examples                                                                             8      Bal   --   5    --  0.05 150  0.50  1500                               9      Bal   --   3    10  0.02 None --      0                                10     Bal   0.01 15   --  0.03 160  0.55   900                        ______________________________________                                    

In Table 1, Comparative Example No. 6 is pure copper. In thiscomparative example, the copper adhesion area of a specimen is large,and the adhesion of a specimen occurs at a low temperature. InComparative Example 7 with addition of Ag and P in a small amount, theadhesion tendency is somewhat suppressed. When Sn is added in a largeamount (Comparative Examples 8 and 10), the adhesion tendency isfurthermore suppressed. When Pb and Sn are added in combination(Comparative Example No. 9), the adhesion is completely suppressed.Contrary to this , the adhesion is completely suppressed in theinventive Examples 1 through 5 even without addition of Pb.

EXAMPLE 2

The copper-alloy sintered materials having the composition shown inTable 2 were produced by the same method as in Example 1. Seizureresistance of the resultant sintered materials was examined by a pin-ondisc tester shown in FIG. 5. In FIG. 5, 5 is a hydralic cylinder, 6 isoil-feeding pads, 7 is a testing specimen, 8 is a disc, which is theopposite material of sliding, 9 is a balance weight which balances withthe hydraulic cylinder, and 10 is a load cell.

The testing conditions were as follows.

(a) Sliding Speed: 15 m/sec

(b) Load: successively load increase (step mode), 600N/min

(c) Grade of Oil: 10W-30

(d) Temperature of Oil: Room Temperature

(e) Opposite Material: Quenched S55C (Hv=550-650), Roughness-0.5-0.8μmRz

(f) Specimen: area-1 cm², roughness-0.1-1.5 μm Rz.

The testing results of seizure resistance are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Composition               Seizure Test                                        (wt/%)                    Seizure Load                                        No.         Cu    Ag     Sn    Pb  P    (kg/cm.sup.2)                         ______________________________________                                        Examples                                                                              11      Bal   0.1  3     --  0.03 860                                         12      Bal   1.0  5     --  --   900                                         13      Bal   2.0  10    --  --   830                                         14      Bal   0.5  5     --  0.05 880                                         15      Bal   1.5  1     --  0.01 850                                 Comparative                                                                           16      Bal   --   --    --  --   400                                 Examples                                                                              17      Bal   0.08 --    --  --   450                                         18      Bal   --   15    --  --   420                                         19      Bal   0.05 0.5   --  --   480                                         20      Bal   --   3.5   24  0.02 450                                         21      Bal   5    8     --  0.03 480                                 ______________________________________                                    

In Table 2, Comparative Example 20 is an example of representativecompositions of a conventional kelmet. When compared with theperformance of this comparative example, it is seen that the seizureresistance of the inventive Examples 11-15 is improved by slightly lessthan twice. It is noticeable that notwithstanding the non-inclusion ofPb in the materials of the inventive examples, the seizure resistance isimproved.

The single addition of Ag (Comparative Example 17) and Sn (ComparativeExample 18) improves the seizure resistance more than that of the purecopper (Comparative Example 16) but to a slight degree. When Ag and Snare added in combination (Comparative Example 19), the seizureresistance is further improved. The degree of improvement is stillslight since P is absent. In Comparative Example 21, since the Agcontent is too high, the seizure resistance is not satisfactory.

EXAMPLE 3

The copper-based sliding-bearing materials having a composition shown inTable 3 were prepared by the same method as in Example 1. Slidingbearings for connecting-rod bearings of a Diesel engine equipped with aturbo-charger (displacement -2400 cc) were manufactured. The backingmetal used was a steel sheet (SPCC, thickness=1.2 mm). The thickness oflining was 0.3 mm. An overlay was directly deposited on the liningsurface without the intermediary of an nickel barrier. The method forforming the overlay was a combination of electric plating with the aidof a borofluoride bath and the diffusion of In in the case of metallicoverlay. A mixture of solid lubricant and resin is baked in the case ofthe solid-lubricant based overlay. The sliding properties of therespective sliding bearings were measured by the following method.

(a) Rotation number: 400 rpm

(b) Unit load of bearing: 40, 60, 70 Mpa

(c) Grade of oil: 10W-30, CD

(d) Temperature of oil: 125° C.

(e) Testing time: 400 h

Evaluation of test results: the wear amount was measured, and averagevalue was calculated; the surface state: acceptable (O), if re-use isdeemed possible under visual inspection, and failure (x), if the re-useis not possible.

                                      TABLE 3                                     __________________________________________________________________________    Results of Engine Test                                                                                            Surface      Wear     Surface                                      Overlay    Coating Thick-                                                                             Amount   State of            Lining Component     Ni  Component  Material                                                                              ness of                                                                            (mg)     Bearing             (wt/%)               Plat-                                                                             (wt/%)         Lubri-                                                                            Overlay                                                                            45 60 70 After               No      Cu Ag Sn                                                                              Pb                                                                              P  ing Pb  Sn In                                                                              Cu                                                                              Resin                                                                             cant                                                                              (μm)                                                                            MPa                                                                              MPa                                                                              MPa                                                                              400                 __________________________________________________________________________                                                              h                   Examples                                                                            22                                                                              Bal                                                                              0.1                                                                              1 --                                                                              0.03                                                                             None                                                                              Bal 10   2 --  --  5    27 33 38 ∘             23                                                                              Bal                                                                              1.0                                                                              5 --                                                                              -- None                                                                              Bal 10 10                                                                              2 --  --  10   40 44 49 ∘             24                                                                              Bal                                                                              1.0                                                                              1 --                                                                              -- None                                                                              Bal 10 10                                                                              2 --  --  3    21 25 32 ∘             25                                                                              Bal                                                                              1.0                                                                              5 --                                                                              -- None                                                                              Bal -- 10                                                                              --                                                                              --  --  5    30 35 41 ∘             26                                                                              Bal                                                                              2.0                                                                              10                                                                              --                                                                              0.05                                                                             None                                                                              Bal -- 10                                                                              2 --  --  25   50 59 64 ∘             27                                                                              Bal                                                                              2.0                                                                              1 --                                                                              -- None                                                                              Bal 10 10                                                                              --                                                                              --  --  5    25 34 39 ∘             28                                                                              Bal                                                                              2.0                                                                              5 --                                                                              -- None                                                                              Bal 10 10                                                                              --                                                                              --  --  1    12 20 29 ∘             29                                                                              Bal                                                                              2.0                                                                              3 --                                                                              -- None                                                                              --  Bal                                                                              --                                                                              --                                                                              --  --  5    23 33 40 ∘             30                                                                              Bal                                                                              2.0                                                                              10                                                                              --                                                                              0.1                                                                              None           PI  MoS.sub.2                                                                         5    18 25 33 ∘             31                                                                              Bal                                                                              2.0                                                                              7 --                                                                              -- None           PAI MoS.sub.2                                                                         10   26 30 38 ∘             32                                                                              Bal                                                                              0.5                                                                              7 --                                                                              0.5                                                                              None           Epoxy                                                                             MoS.sub.2                                                                         5    16 23 31 ∘                                           Resin                                           33                                                                              Bal                                                                              1.0                                                                              3 --                                                                              -- None           PI  MoS.sub.2                                                                         3    14 21 28 ∘       Comparative                                                                         34                                                                              Bal                                                                              -- 5 25                                                                              -- None                                                                              Bal -- 10  --  --  5    Sei-                                                                             Sei-                                                                             Sei-                                                                             x                   Examples                                         zure                                                                             zure                                                                             zure                                                                    at at at                                                                      310 h                                                                            170                                                                              100 h                        35                                                                              Bal                                                                              0.05                                                                             5 --                                                                              -- None                                                                              Bal 10 10  --  --  5    Sei-                                                                             Sei-                                                                             Sei-                                                                             x                                                                    zure                                                                             zure                                                                             zure                                                                    at at at                                                                      150 h                                                                            100                                                                              70 h                         36                                                                              Bal                                                                              1.0                                                                              15     None                                                                              Bal 10 10                                                                              --                                                                              --  --  5    Sei-                                                                             Sei-                                                                             Sei-                                                                             x                                                                    zure                                                                             zure                                                                             zure                                                                    at at at                                                                      70 h                                                                             50 h                                                                             30 h                         37                                                                              Bal                                                                              3.0                                                                              --     None                                                                              Bal 10 10                                                                              --                                                                              --  --  5    Sei-                                                                             Sei-                                                                             Sei-                                                                             x                                                                    zure                                                                             zure                                                                             zure                                                                    at at at                                                                      100 h                                                                            80 h                                                                             50                     __________________________________________________________________________                                                           h                  

In Table 3, Comparative Example 34 is an ordinary kelmet bearing fittedwith an overlay, the thickness of which is so thin as to only providethe compatibility. Seizure occurs under the present testing condition.In Comparative Example 35, in which a small amount (0.05%) of Ag isadded, and Pb is removed, seizure becomes more likely to occur. InComparative Example 36, in which the Ag content is further increased anda large amount of Sn is added, and in Comparative Example 36, in whichonly Ag is added in a large amount, seizure becomes somewhat less likelyto occur.

Compared with these comparative examples, the inventive examples exhibitvery small wear amount and improved seizure resistance. Particularly,the properties are improved, even if the Sn content is very small(Examples 22 and 24).

INDUSTRIAL APPLICABILITY

As is described hereinabove, the Cu--Sn--Ag based copper-alloy accordingto the present invention is characterized in the points that the seizureresistance required for the sliding bearing are greatly improved and,further, is free of lead, which causes the corrosion due to the degradedoil, or the lead addition amount is low.

The copper alloy having the present composition is conventionally knownto be used as spring or contact material for electric parts (forexample, Japanese Unexamined Patent Publication (Kokai) No. Sho49-75,417, No. Sho 50-77,216, No. Hei 2-228,439, and No. Hei 5-195,173).The present inventive material, in which the Ag and Sn, which areforcedly solid-dissolved and then precipitate on the sliding surfaceduring the use of a bearing, is remarkable as compared with the knownmaterials from the point of view of metallographic structure control.

We claim:
 1. A copper-based sliding bearing material having improvedseizure resistance, consisting of, by weight percentage, from 0.1 to 2%of Ag, from 1 to 10% of Sn, and the balance consisting of Cu andunavoidable impurities, and, further said Ag and Sn do not essentiallyform secondary phases but are in complete or essentially solid-solutionstate in a Cu matrix.
 2. A copper-based sliding bearing materialaccording to claim 1, where the Ag content is from 0.4 to 1%.
 3. Acopper-based sliding bearing material according to claim 1, where the Sncontent is from 2 to 7%.
 4. A sliding bearing for an internal combustionengine which comprises copper-based sliding material according to claim1, and an overlay, having a thickness of from 1 to 25 μm, which consistsof soft metal or solid lubricant and resin.
 5. A sliding bearing for aninternal combustion engine according to claim 4, wherein the thicknessof the overlay is from 2-8 μm.
 6. A sliding bearing for an internalcombustion engine according to claim 4, wherein the overlay is directlybonded on the above-mentioned sliding bearing material without theintermediary of an intermediate layer.
 7. A sliding bearing for aninternal combustion engine according to claim 1, where said complete oressentially solid solution state is maintained except for a slidingsurface with a shaft.
 8. A copper-based sliding bearing material havingimproved seizure resistance, consisting of, by weight percentage, from0.1 to 2% of Ag, from 1 to 10% of Sn, not more than 0.5% of P and thebalance consisting of Cu and unavoidable impurities, and, further saidAg and Sn do not essentially form secondary phases but are in completeor essentially solid-solution state in a Cu matrix.
 9. A copper-basedsliding bearing material according to claim 8, where the Ag content isfrom 0.4 to 1%.
 10. A copper-based sliding bearing material according toclaim 8, where the Sn content is from 2 to 7%.
 11. A copper-basedsliding bearing material according to claim 8, where the P content isfrom 0.5 to 0.15%.
 12. A sliding bearing for an internal combustionengine which comprises copper-based sliding material according to claim8, and an overlay, having a thickness of from 1 to 25 μm, which consistsof soft metal or solid lubricant and resin.
 13. A sliding bearing for aninternal combustion engine according to claim 12, wherein the thicknessof the overlay is from 2-8 μm.
 14. A sliding bearing for an internalcombustion engine according to claim 12, wherein the overlay is directlybonded on the above-mentioned sliding bearing material without theintermediary of an intermediate layer.
 15. A sliding bearing for aninternal combustion engine according to claim 12, where said complete oressentially solid solution state is maintained except for a slidingsurface with a shaft.
 16. A copper-based sliding bearing material havingimproved seizure resistance, consisting of, by weight percentage, from0.1 to 2% of Ag, from 1 to 10% of Sn, not more than 4% of at least oneelement selected from the group consisting of Pb and Bi, and the balanceconsisting of Cu and unavoidable impurities, and, further said Ag and Sndo not essentially form secondary phases but are in complete oressentially solid-solution state in a Cu matrix.
 17. A copper-basedsliding bearing material according to claim 16, where the Ag content isfrom 0.4 to 1%.
 18. A copper-based sliding bearing material according toclaim 16, where the Sn content is from 2 to 7%.
 19. A sliding bearingfor an internal combustion engine which comprises copper-based slidingmaterial according to claim 16, and an overlay, having a thickness offrom 1 to 25 μm, which consists of soft metal or solid lubricant andresin.
 20. A sliding bearing for an internal combustion engine accordingto claim 19, wherein the thickness of the overlay is from 2-8 μm.
 21. Asliding bearing for an internal combustion engine according to claim 19,wherein the overlay is directly bonded on the above-mentioned slidingbearing material without the intermediary of an intermediate layer. 22.A sliding bearing for an internal combustion engine according to claim19, where said complete or essentially solid solution state ismaintained except for a sliding surface with a shaft.
 23. A copper-basedsliding bearing material having improved seizure resistance, consistingof, by weight percentage, from 0.1 to 2% of Ag, from 1 to 10% of Sn, notmore than 0.5% of P, not more than 4% of at least one element selectedfrom the group consisting of Pb and Bi, and the balance consisting of Cuand unavoidable impurities, and, further said Ag and Sn do notessentially form secondary phases but are in complete or essentiallysolid-solution state in a Cu matrix.
 24. A copper-based sliding bearingmaterial according to claim 23, where the Ag content is from 0.4 to 1%.25. A copper-based sliding bearing material according to claim 23, wherethe Sn content is from 2 to 7%.
 26. A copper-based sliding bearingmaterial according to claim 23, where the P content is from 0.5 to0.15%.
 27. A sliding bearing for an internal combustion engine whichcomprises copper-based sliding material according to claim 23, and anoverlay, having a thickness of from 1 to 25 μm, which consists of softmetal or solid lubricant and resin.
 28. A sliding bearing for aninternal combustion engine according to claim 27, wherein the thicknessof the overlay is from 2-8 μm.
 29. A sliding bearing for an internalcombustion engine according to claim 27, wherein the overlay is directlybonded on the above-mentioned sliding bearing material without theintermediary of an intermediate layer.
 30. A sliding bearing for aninternal combustion engine according to claim 27, where said complete oressentially solid solution state is maintained except for a slidingsurface with a shaft.